Lubricant composition

ABSTRACT

A lubricating oil composition containing a base oil (A) and a thiadiazole-based compound (B). A content of a sulfurized olefin is less than 0.20 mass % based on the total amount of the lubricating oil composition, and a kinematic viscosity of the lubricating oil composition at 100° C. is 2.1 mm 2 /s or more and less than 5.0 mm 2 /s.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition, use of a lubricating oil composition, and a method for producing a lubricating oil composition.

BACKGROUND ART

Various apparatuses such as an engine, a transmission, a speed reducer, a compressor and a hydraulic system have mechanisms such as a torque converter, a wet clutch, a gear bearing mechanism, an oil pump and a hydraulic control mechanism. In these mechanisms, lubricating oil compositions are used, and lubricating oil compositions capable of meeting various requirements have been developed.

For example, Patent Literature 1 discloses a gear oil composition comprising: a base oil comprising a blend of a low-viscosity mineral oil-based lubricating base oil and a high-viscosity solvent-refined mineral oil-based lubricating oil in a predetermined ratio; and a zinc dialkyldithiophosphate and an alkaline earth metal-based detergent in predetermined amounts, for the purpose of providing a gear oil composition having a fuel saving performance and providing gears, bearings, etc. with sufficient durability.

CITATION LIST Patent Literature

-   Patent Literature 1: JP-A-2012-193255

SUMMARY OF INVENTION Technical Problem

By the way, for example, a lubricating oil composition used for various apparatuses such as an electric motor sometimes requires not only insulation properties but also, depending on the mode of the apparatus, characteristics of cooling performance, scuffing resistance, etc. That is to say, a novel lubricating oil composition having characteristics (e.g., cooling performance, scuffing resistance, insulation properties) suitable for lubrication meeting various mechanisms incorporated in apparatuses has been desired.

Solution to Problem

The present invention provides a lubricating oil composition comprising a base oil and a thiadiazole-based compound and having been adjusted in such a manner that a content of a sulfurized olefin is less than a predetermined value and that a kinematic viscosity of the lubricating oil composition at 100° C. is in a specific range. Specifically, the present invention provides lubricating oil compositions according to the following embodiments [1] to [12], use of a lubricating oil composition according to the following embodiment [13], and a method for producing a lubricating oil composition according to the following embodiment [14].

-   -   [1] A lubricating oil composition comprising a base oil (A) and         a thiadiazole-based compound (B), wherein         -   a content of a sulfurized olefin is less than 0.20 mass %             based on the total amount of the lubricating oil             composition, and         -   a kinematic viscosity of the lubricating oil composition at             100° C. is 2.1 mm²/s or more and less than 5.0 mm²/s.     -   [2] The lubricating oil composition according to the above [1],         wherein the component (B) comprises a thiadiazole-based compound         (B1) having a branched chain alkyl group.     -   [3] The lubricating oil composition according to the above [2],         wherein the number of carbon atoms of the branched chain alkyl         group of the component (B1) is 5 or more.     -   [4] The lubricating oil composition according to any one of the         above [1] to [3], wherein the component (B) comprises a compound         represented by any one of the following general formulae (b-1)         to (b-4):

wherein R¹ and R² are each independently a hydrocarbon group, and m and n are each independently an integer of 1 to 10.

-   -   [5] The lubricating oil composition according to the above [4],         wherein R¹ and R² are each independently a branched chain alkyl         group having 5 or more carbon atoms.     -   [6] The lubricating oil composition according to any one of the         above [1] to [5], wherein a content of a compound represented by         the following general formula (b-x) is less than 10 mass % based         on the total amount of the component (B) contained in the         lubricating oil composition,

wherein R^(a) is a hydrogen atom or a methyl group, R^(b) is an alkyl group having 1 to 4 carbon atoms, and p is 0 or 1.

-   -   [7] The lubricating oil composition according to any one of the         above [1] to [6], wherein a content of the component (B) is 0.01         to 3.0 mass % based on the total amount of the lubricating oil         composition.     -   [8] The lubricating oil composition according to any one of the         above [1] to [6], wherein a content of the component (B) is 0.10         to 1.0 mass % based on the total amount of the lubricating oil         composition.     -   [9] The lubricating oil composition according to any one of the         above [1] to [8], wherein the component (A) is one or more         selected from mineral oils classified in Group II and Group III         of API base oil categories, and synthetic oils.     -   [10] The lubricating oil composition according to any one of the         above [1] to [9], further comprising one or more         phosphorus-based compounds (C) selected from a phosphoric acid         ester and a phosphorous acid ester.     -   [11] The lubricating oil composition according to the above         [10], wherein the component (C) comprises one or more         sulfur-phosphorus-based compounds (C1) selected from a sulfur         atom-containing phosphoric acid ester and a sulfur         atom-containing phosphorous acid ester.     -   [12] The lubricating oil composition according to any one of the         above [1] to [11], being used for lubrication of a speed         reducer.     -   [13] Use of a lubricating oil composition, wherein the         lubricating oil composition according to any one of the above         [1] to is applied to lubrication of a speed reducer.     -   [14] A method for producing the lubricating oil composition         according to any one of the above [1] to [12], comprising         -   adding a thiadiazole-based compound (B) to a base oil (A),             and         -   preparing the lubricating oil composition in such a manner             that a content of a sulfurized olefin is less than mass %             based on the total amount of the lubricating oil             composition, and that         -   a kinematic viscosity of the lubricating oil composition at             100° C. is 2.1 mm²/s or more and less than mm²/s.

Advantageous Effects of Invention

The lubricating oil composition of one preferred embodiment of the present invention is a lubricating oil composition having characteristics suitable for various mechanisms incorporated in apparatuses, and the lubricating oil composition of a more preferred embodiment of the present invention can be improved in cooling performance, scuffing resistance and insulation properties in a balanced manner. On that account, these lubricating oil compositions can be preferably used for lubrication of a speed reducer, etc.

DESCRIPTION OF EMBODIMENTS

Regarding the numerical range described in the present specification, the upper limit and the lower limit can be arbitrarily combined. For example, with the description “preferably 30 to 100, more preferably 40 to 80” as a numerical range, the range of “30 to 80” and the range of “40 to 100” are also included in the numerical range described in the present specification. Alternatively, for example, with the description “preferably 30 or more, more preferably 40 or more, and preferably 100 or less, more preferably 80 or less” as a numerical range, the range of “30 to 80” and the range of “40 to 100” are also included in the numerical range described in the present specification.

In addition, for example, the description of “60 to 100” as the numerical range described in the present specification means a range of “60 or more and 100 or less”.

In the present specification, the kinematic viscosity and the viscosity index mean values measured or calculated in accordance with JIS K2283:2000.

[Constitution of Lubricating Oil Composition]

The lubricating oil composition of one embodiment of the present invention comprises a base oil (A) (also referred to as a “component A” hereinafter) and a thiadiazol-based compound (also referred to as a “component (B)” hereinafter), and satisfies the following requirements (I) and (II).

-   -   Requirement (I): a content of a sulfurized olefin is less than         0.20 mass % based on the total amount (100 mass %) of the         lubricating oil composition.     -   Requirement (II): a kinematic viscosity of the lubricating oil         composition at 100° C. is 2.1 mm²/s or more and less than 5.0         mm²/s.

According to the study by the present inventors, it has been found that the lower the kinematic viscosity of a lubricating oil composition is, the better the cooling performance becomes. A lubricating oil composition excellent in cooling performance can be preferably used for cooling of an apparatus accompanied by generation of heat, such as an electric motor or an electric generator.

In the lubricating oil composition having a low kinematic viscosity, however, localized surface damage called scuffing, which is due to solid phase adhesion occurring on a sliding contact surface such as a tooth surface, tends to occur, and besides, reduction of volume resistivity is also observed, and a problem of insulation properties also occurs.

Then, in the present invention, by preparing the lubricating oil composition in such a manner that the kinematic viscosity of the lubricating oil composition is in the range satisfying the requirement (II), cooling performance and insulation properties are improved, and by preparing the lubricating oil composition in such a manner that the lubricating oil composition contains a thiadiazole-based compound that is the compound (B) and that the content of a sulfurized olefin is in the range satisfying the requirement (I), scuffing resistance is improved while cooling performance and insulation properties are favorably maintained.

As a result, the lubricating oil composition of one embodiment of the present invention can become a lubricating oil composition having been improved in cooling performance, scuffing resistance and insulation properties in a balanced manner.

As the sulfurized olefin specified in the requirement (I), for example, a compound represented by the following general formula (i) can be mentioned.

R—(S)_(q)—R′  (i)

In the formula (i), R is an alkenyl group having 2 to 20 carbon atoms, R′ is an alkenyl group having 2 to 20 carbon atoms or an alkyl group having 2 to 20 carbon atoms, and q is an integer of 1 to 10.

As specified in the requirement (I), the content of the sulfurized olefin is less than 0.20 mass % based on the total amount (100 mass %) of the lubricating oil composition, but from the viewpoint of obtaining a lubricating oil composition having been not only more improved in scuffing resistance but also improved in copper corrosion prevention, it is preferably less than 0.18 mass %, more preferably less than 0.15 mass %, still more preferably less than 0.12 mass %, still much more preferably less than 0.10 mass %, and particularly preferably less than 0.07 mass %, or may be less than 0.05 mass %, less than 0.04 mass %, less than 0.03 mass %, less than 0.02 mass %, less than 0.01 mass %, or less than 0.001 mass %.

As specified in the requirement (II), the kinematic viscosity of the lubricating oil composition at 100° C. is 2.1 mm²/s or more, but from the viewpoint of obtaining a lubricating oil composition having been more improved in insulation properties and having a low flash point and excellent handling properties, it is preferably 2.2 mm²/s or more, more preferably 2.4 mm²/s or more, still more preferably 2.5 mm²/s or more, still much more preferably 2.7 mm²/s or more, and particularly preferably 2.8 mm²/s or more, or may be 3.0 mm²/s or more, 3.2 mm²/s or more, 3.4 mm²/s or more, or 3.6 mm²/s or more.

The kinematic viscosity of the lubricating oil composition at 100° C. is less than 5.0 mm²/s, but from the viewpoint of obtaining a lubricating oil composition having been more improved in cooling performance, it is preferably 4.8 mm²/s or less, more preferably 4.5 mm²/s or less, more preferably 4.2 mm²/s or less, still more preferably 4.1 mm²/s or less, still more preferably 3.9 mm²/s or less, still much more preferably 3.7 mm²/s or less, still much more preferably 3.5 mm²/s or less, and particularly preferably 3.2 mm²/s or less, or may be 3.0 mm²/s or less, 2.8 mm²/s or less, or 2.6 mm²/s or less.

The lubricating oil composition of one embodiment of the present invention preferably further contains one or more phosphorus-based compounds (C) (also referred to as a “component (C)” hereinafter) selected from a phosphoric acid ester and a phosphorous acid ester, from the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance.

The lubricating oil composition of one embodiment of the present invention may further contain various additives other than the components (B) to (C) when needed as long as the effects of the present invention are not impaired.

In the lubricating oil composition of one embodiment of the present invention, the total content of the components (A) and (B) is preferably 50 mass % or more, more preferably 60 mass % or more, still more preferably 70 mass % or more, still much more preferably 75 mass % or more, and particularly preferably 80 mass % or more, or may be 85 mass % or more, 90 mass % or more, or 92 mass % or more, and it may be 100 mass % or less, 99.5 mass % or less, 99.0 mass % or less, 98.5 mass % or less, 98.0 mass % or less, 97.5 mass % or less, 97.0 mass % or less, 96.5 mass % or less, or 96.0 mass % or less, based on the total amount (100 mass %) of the lubricating oil composition.

In the lubricating oil composition of one embodiment of the present invention, the total content of the components (A), (B) and (C) is preferably 52 mass % or more, more preferably 62 mass % or more, still more preferably 72 mass % or more, still much more preferably 77 mass % or more, and particularly preferably 82 mass % or more, or may be 87 mass % or more, 90 mass % or more, 92 mass % or more, or 94 mass % or more, and it may be 100 mass % or less, 99.5 mass % or less, 99.0 mass % or less, 98.5 mass % or less, 98.0 mass % or less, 97.5 mass % or less, 97.0 mass % or less, 96.5 mass % or less, or 96.0 mass % or less, based on the total amount (100 mass %) of the lubricating oil composition.

Details of the components contained in the lubricating oil composition of one embodiment of the present invention will be described hereinafter.

<Component (A): Base Oil>

As the base oil that is the component (A) used in one embodiment of the present invention, one or more selected from mineral oils and synthetic oils can be mentioned.

Examples of the mineral oils include atmospheric residues obtained by subjecting crude oils, such as paraffinic crude oil, intermediate base crude oil and naphthenic crude oil, to atmospheric distillation; distillates obtained by subjecting these atmospheric residues to vacuum distillation; and refined oils obtained by subjecting the distillates to one or more of refining treatments, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining (hydrocracking).

Examples of the synthetic oils include poly-α-olefins, such as an α-olefin homopolymer and an α-olefin copolymer (for example, an α-olefin copolymer having 8 to 14 carbon atoms such as an ethylene-α-olefin copolymer); isoparaffin; polyalkylene glycol; ester oils, such as polyol ester, dibasic acid ester, and phosphoric acid ester; ether oils, such as polyphenyl ether; alkylbenzene; alkylnaphthalene; and synthetic oil (GTL) obtained by isomerizing wax (GTL WAX (Gas To Liquids WAX)) produced from natural gas through Fischer-Tropsch process or the like.

The component (A) used in one embodiment of the present invention preferably contains one or more selected from mineral oils classified in Group II and Group III of API (American Petroleum Institute) base oil categories, and synthetic oils, and more preferably contains one or more selected from mineral oils classified in group III, and synthetic oils.

From the viewpoint of preparing a lubricating oil composition satisfying the requirement (II), the kinematic viscosity of the component (A) used in one embodiment of the present invention at 100° C. is preferably 1.9 mm²/s or more, more preferably 2.0 mm²/s or more, more preferably 2.1 mm²/s or more, still more preferably 2.3 mm²/s or more, still much more preferably 2.5 mm²/s or more, and particularly preferably 2.7 mm²/s or more, or may be 2.9 mm²/s or more, 3.0 mm²/s or more, 3.2 mm²/s or more, 3.4 mm²/s or more, or 3.6 mm²/s or more.

The kinematic viscosity of the component (A) at 100° C. is preferably 5.0 mm²/s or less, more preferably 4.8 mm²/s or less, more preferably 4.6 mm²/s or less, still more preferably 4.5 mm²/s or less, still more preferably 4.3 mm²/s or less, still much more preferably 4.2 mm²/s or less, still much more preferably 4.0 mm²/s or less, and particularly preferably 3.8 mm²/s or less, or may be 3.7 mm²/s or less, 3.6 mm²/s or less, 3.5 mm²/s or less, 3.4 mm²/s or less, 3.3 mm²/s or less, 3.2 mm²/s or less, 3.0 mm²/s or less, 2.8 mm²/s or less, or 2.6 mm²/s or less.

The viscosity index of the component (A) used in one embodiment of the present invention is preferably 70 or more, more preferably 80 or more, still more preferably 90 or more, and still much more preferably 100 or more.

When a mixed oil that is a combination of two or more base oils is used as the component (A) in one embodiment of the present invention, the kinematic viscosity and the viscosity index of the mixed oil are preferably in the above ranges. On that account, by using a low-viscosity base oil and a high-viscosity base oil in combination, the mixed oil may be prepared so as to have a kinematic viscosity and a viscosity index in the above ranges.

In the lubricating oil composition of one embodiment of the present invention, the content of the component (A) is preferably 45 mass % or more, more preferably 50 mass % or more, still more preferably 55 mass % or more, still much more preferably 60 mass % or more, and particularly preferably 65 mass % or more, or may be 70 mass % or more, 75 mass % or more, 80 mass % or more, 85 mass % or more, 90 mass % or more, or 92 mass % or more, and it is preferably 99.99 mass % or less, more preferably 99.90 mass % or less, still more preferably 99.50 mass % or less, still much more preferably 99.00 mass % or less, and particularly preferably 98.50 mass % or less, or may be 98.00 mass % or less, 97.50 mass % or less, 97.00 mass % or less, 96.50 mass % or less, or 96.00 mass % or less, based on the total amount (100 mass %) of the lubricating oil composition.

<Component (B): Thiadiazole-Based Compound>

The thiadiazole-based compound that is the component (B) used in one embodiment of the present invention may be any compound as long as it is a compound having a thiadiazole ring, but from the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance, it preferably contains a compound represented by any one of the following general formulae (b-1) to (b-4), and more preferably contains at least a compound represented by the following general formula (b-1).

The component (B) may be used singly, or may be used in combination of two or more.

In the above formulae, R¹ and R² are each independently a hydrocarbon group.

m and n are each independently an integer of 1 to 10, but from the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance, they are each independently preferably an integer of 1 to 6, more preferably an integer of 1 to 4, still more preferably an integer of 2 to 3, and still much more preferably 2.

Examples of the hydrocarbon groups capable of being selected as R¹ and R² include straight-chain or branched chain alkyl groups, such as a methyl group, an ethyl group, a propyl group (n-propyl group, isopropyl group), a butyl group (n-butyl group, s-butyl group, t-butyl group, isobutyl group), a pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a 1,1-dimethylheptyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group and an octadecyl group; straight-chain or branched chain alkenyl groups, such as an ethenyl group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group and a pentadecenyl group; cycloalkyl groups which may have an alkyl group, such as a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a propylcyclohexyl group, a butylcyclohexyl group and a heptylcyclohexyl group; aryl groups, such as a phenyl group, a naphthyl group, an anthracenyl group, a biphenyl group and a terphenyl group; alkylaryl groups, such as a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, and a dimethylnaphthyl group; and arylalkyl groups, such as a phenylmethyl group, a phenylethyl group and a diphenylmethyl group.

From the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance, the number of carbon atoms of the hydrocarbon group capable of being selected as R¹ and R² is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and still much more preferably 5 or more, or may be 7 or more, 8 or more, or 9 or more, and it is preferably 30 or less, more preferably 24 or less, more preferably 20 or less, more preferably 18 or less, still more preferably 16 or less, still more preferably 14 or less, and still much more preferably 12 or less, or may be 11 or less, or 10 or less.

From the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance, R¹ and R² are each independently preferably an alkyl group among these, and from the viewpoint of obtaining a lubricating oil composition capable of effectively suppressing elution of copper by being improved in copper corrosion prevention together with scuffing resistance, they are each independently more preferably a branched chain alkyl group, and still more preferably a branched chain alkyl group having 5 or more carbon atoms.

From the above viewpoint, the number of carbon atoms of the branched chain alkyl group is preferably 5 or more, but it is more preferably 7 or more, still more preferably 8 or more, and still much more preferably 9 or more, and it is preferably 30 or less, more preferably 24 or less, more preferably 20 or less, more preferably 18 or less, still more preferably 16 or less, still more preferably 14 or less, and still much more preferably 12 or less, or may be 11 or less, or 10 or less.

In the lubricating oil composition of one embodiment of the present invention, the total content of the compounds each of which is represented by any one of the general formulae (b-1) to (b-4) is preferably 60 to 100 mass %, more preferably 70 to 100 mass %, still more preferably 80 to 100 mass %, still much more preferably 90 to 100 mass %, and particularly preferably 95 to 100 mass %, based on the total amount (100 mass %) of the component (B) contained in the lubricating oil composition, from the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance.

In the lubricating oil composition of one embodiment of the present invention, the content of the compound represented by the general formula (b-1) is preferably 50 to 100 mass %, more preferably 60 to 100 mass %, still more preferably 70 to 100 mass %, still much more preferably 80 to 100 mass %, and particularly preferably 90 to 100 mass %, based on the total amount (100 mass %) of the component (B) contained in the lubricating oil composition, from the above viewpoint.

In the lubricating oil composition of one embodiment of the present invention, the content of a compound represented by the following general formula (b-x) is preferably less than 10 mass %, more preferably less than 8 mass %, still more preferably less than 5 mass %, still much more preferably less than 3 mass %, and particularly preferably less than 1 mass %, based on the total amount (100 mass %) of the component (B) contained in the lubricating oil composition.

wherein R^(a) is a hydrogen atom or a methyl group, R^(b) is an alkyl group having 1 to 4 carbon atoms, and p is 0 or 1.

In the lubricating oil composition of one embodiment of the present invention, the component (B) preferably contains a thiadiazole-based compound (B1) (also referred to as a “component (B1)” hereinafter) having a branched chain alkyl group, from the viewpoint of obtaining a lubricating oil composition capable of effectively suppressing elution of copper by being improved in copper corrosion prevention together with scuffing resistance.

From the above viewpoint, the content of the component (B1) is preferably 50 to 100 mass %, more preferably 60 to 100 mass %, more preferably 70 to 100 mass %, still more preferably 80 to 100 mass %, still much more preferably 90 to 100 mass %, and particularly preferably 95 to 100 mass %, based on the total amount (100 mass %) of the component (B) contained in the lubricating oil composition.

From the viewpoint of obtaining a lubricating oil composition capable of effectively suppressing elution of copper by being improved in copper corrosion prevention together with scuffing resistance, the number of carbon atoms of the branched chain alkyl group of the component (B1) is preferably 5 or more, more preferably 7 or more, still more preferably 8 or more, and still much more preferably 9 or more, and it is preferably 30 or less, more preferably 24 or less, more preferably 20 or less, more preferably 18 or less, still more preferably 16 or less, still more preferably 14 or less, and still much more preferably 12 or less, or may be 11 or less, or 10 or less.

From the viewpoint of obtaining a lubricating oil composition capable of effectively suppressing elution of copper by being improved in copper corrosion prevention together with scuffing resistance, the component (B1) is preferably a compound represented by any one of the general formulae (b-1) to (b-4) wherein R¹ and R² are each independently a branched chain alkyl group, and is more preferably a compound represented by the general formula (b-1) wherein R¹ and R² are each independently a branched chain alkyl group. A preferred range of the number of carbon atoms of the branched chain alkyl group is as previously described.

From the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance, the content of the component (B) in the lubricating oil composition of one embodiment of the present invention is preferably 0.01 mass % or more, more preferably 0.05 mass % or more, still more preferably 0.07 mass % or more, still much more preferably 0.10 mass % or more, and particularly preferably 0.15 mass % or more, or may be 0.17 mass % or more, 0.20 mass % or more, 0.23 mass % or more, 0.25 mass % or more, 0.27 mass % or more, 0.30 mass % or more, 0.32 mass % or more, 0.35 mass % or more, or mass % or more, and it is preferably 3.0 mass % or less, more preferably 2.5 mass % or less, still more preferably 2.0 mass % or less, still much more preferably 1.5 mass % or less, and particularly preferably 1.2 mass % or less, or may be 1.0 mass % or less, 0.95 mass % or less, mass % or less, 0.85 mass % or less, 0.80 mass % or less, 0.75 mass % or less, 0.70 mass % or less, 0.65 mass % or less, 0.60 mass % or less, 0.55 mass % or less, or 0.50 mass % or less, based on the total amount (100 mass %) of the lubricating oil composition.

For example, the content of the component (B) is to 3.0 mass %, 0.05 to 2.5 mass %, 0.07 to 2.0 mass %, to 1.5 mass %, 0.10 to 1.2 mass %, 0.10 to 1.0 mass %, or 0.15 to 1.0 mass %, based on the total amount (100 mass %) of the lubricating oil composition.

From the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance, the content of the component (B) in terms of sulfur atoms in the lubricating oil composition of one embodiment of the present invention is preferably 30 ppm by mass or more, more preferably 50 ppm by mass or more, still more preferably 100 ppm by mass or more, still much more preferably 200 ppm by mass or more, and particularly preferably 300 ppm by mass or more, or may be 400 ppm by mass or more, 500 ppm by mass or more, 600 ppm by mass or more, 700 ppm by mass or more, 800 ppm by mass or more, 900 ppm by mass or more, 1000 ppm by mass or more, 1050 ppm by mass or more, or 1100 ppm by mass or more, and it is preferably 10000 ppm by mass or less, more preferably 8000 ppm by mass or less, still more preferably 7000 ppm by mass or less, still much more preferably 6000 ppm by mass or less, and particularly preferably 5000 ppm by mass or less, or may be 4500 ppm by mass or less, 4000 ppm by mass or less, 3500 ppm by mass or less, 3000 ppm by mass or less, 2500 ppm by mass or less, 2200 ppm by mass or less, 2000 ppm by mass or less, 1800 ppm by mass or less, 1700 ppm by mass or less, 1600 ppm by mass or less, 1500 ppm by mass or less, or 1400 ppm by mass or less, based on the total amount (100 mass %) of the lubricating oil composition.

In the present specification, the content of sulfur atoms means a value measured in accordance with JIS K2541-6:2013.

From the viewpoint of obtaining a lubricating oil composition having been more improved in scuffing resistance, the content of the component (B) in terms of nitrogen atoms in the lubricating oil composition of one embodiment of the present invention is preferably 10 ppm by mass or more, more preferably 30 ppm by mass or more, still more preferably 50 ppm by mass or more, still much more preferably 70 ppm by mass or more, and particularly preferably 100 ppm by mass or more, or may be 120 ppm by mass or more, 130 ppm by mass or more, 140 ppm by mass or more, 150 ppm by mass or more, 160 ppm by mass or more, 170 ppm by mass or more, 180 ppm by mass or more, 190 ppm by mass or more, or 200 ppm by mass or more, and it is preferably 2000 ppm by mass or less, more preferably 1800 ppm by mass or less, still more preferably 1500 ppm by mass or less, still much more preferably 1200 ppm by mass or less, and particularly preferably 1000 ppm by mass or less, or may be 900 ppm by mass or less, 800 ppm by mass or less, 700 ppm by mass or less, 600 ppm by mass or less, 550 ppm by mass or less, 500 ppm by mass or less, 450 ppm by mass or less, 400 ppm by mass or less, 350 ppm by mass or less, 320 ppm by mass or less, 300 ppm by mass or less, or 280 ppm by mass or less, based on the total amount (100 mass %) of the lubricating oil composition.

In the present specification, the content of nitrogen atoms means a value measured in accordance with JIS K2609.

<Component (C): Phosphorus-Based Compound (C)>

The lubricating oil composition of one embodiment of the present invention preferably further contains one or more phosphorus-based compounds (C) selected from a phosphoric acid ester and a phosphorous acid ester, from the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance.

Examples of the phosphoric acid ester contained as the component (C) in one embodiment of the present invention include a neutral phosphoric acid ester represented by the following general formula (c-1), and an acid phosphoric acid ester represented by the following general formula (c-2) or (c-3).

Examples of the phosphorous acid ester contained as the component (C) in one embodiment of the present invention include an acid phosphorous acid ester represented by the following general formula (c-4) or (c-5).

In the above formulae, each RP′ is independently an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 18 carbon atoms which may be substituted by an alkyl group having 1 to 6 carbon atoms, a group having a sulfide bond, or the like. Multiple RP′ may be the same as one another, or may be different from one another.

Examples of the alkyl groups capable of being selected as R^(A) include a methyl group, an ethyl group, a propyl group (n-propyl group, isopropyl group), a butyl group (n-butyl group, s-butyl group, t-butyl group, isobutyl group), a pentyl group, a hexyl group, a 2-ethylhexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, tridecyl group, a tetradecyl group, a hexadecyl group and an octadecyl group.

These alkyl groups may be straight-chain alkyl groups or may be branched chain alkyl groups.

The number of carbon atoms of the alkyl group is 1 to 30, but it is preferably 3 to 20, more preferably 5 to 16, still more preferably 6 to 14, and still much more preferably 8 to 12.

Examples of the alkenyl groups capable of being selected as R^(A) include an ethenyl group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group and an octadecenyl group.

These alkenyl groups may be straight-chain alkenyl groups or may be branched chain alkenyl groups.

The number of carbon atoms of the alkenyl group is 2 to 20, but it is preferably 3 to 16, and more preferably 6 to 12.

Examples of the aryl groups capable of being selected as R^(A) include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a biphenyl group, a terphenyl group and a phenylnaphthyl group, and preferable is a phenyl group.

Examples of the “alkyl group having 1 to 6 carbon atoms” that can substitute these aryl groups include alkyl groups having 1 to 6 carbon atoms among the aforementioned alkyl groups.

The group having a sulfide bond, which is capable of being selected as R^(A), is preferably a group represented by the following general formula (ii).

*—R^(A02)—S_(x)—R^(A01)  (ii)

In the formula (ii), R^(A01) is a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms. R^(A02) is a divalent organic group. x is an integer of 1 or more, preferably an integer of 1 to 10, more preferably an integer of 1 to 5, still more preferably an integer of 1 to 3, still much more preferably 1 or 2, and particularly preferably 1. * represents a bonding position.

Examples of the monovalent organic groups capable of being selected as R^(A01) include an alkyl group, an alkenyl group and an aryl group, and preferable is an alkyl group having 1 to 20 carbon atoms or a group wherein at least one —CH₂— structure of an alkyl group having 1 to 20 (preferably 2 to 18, more preferably 4 to 16, still more preferably 6 to 12, still much more preferably 8 to 10) carbon atoms has been substituted by —O—, —S—, —COO—, —OCO—, —CSO—, —OCS—, —CH═CH— or —C≡C—, and more preferable is an alkyl group.

The alkyl group capable of being selected as R^(A01) may be a straight-chain alkyl group or may be a branched chain alkyl group, but it is preferably a straight-chain alkyl group.

The number of carbon atoms of the alkyl group is 1 to 20, but it is preferably 2 to 18, more preferably 4 to 16, still more preferably 6 to 12, and still much more preferably 8 to 10.

Examples of the divalent organic groups capable of being selected as R^(A02) include an alkylene group having 1 to 20 carbon atoms, a cycloalkylene group, an alkenylene group having 1 to 20 carbon atoms, a cycloalkenylene group and an arylene group, and preferable is an alkylene group having 1 to 20 carbon atoms or a group wherein at least one —CH₂— structure of an alkylene group having 1 to 20 (preferably 2 to 12, more preferably 2 to 8, still more preferably 2 to 4) carbon atoms has been substituted by —O—, —S—, —COO—, —OCO—, —CSO—, —OCS—, —CH═CH— or —C≡C—, and more preferable is an alkylene group having 2 to 20 carbon atoms.

The alkylene group capable of being selected as R^(A02) may be a straight-chain alkylene group or may be a branched chain alkylene group, but it is preferably a straight-chain alkylene group.

The number of carbon atoms of the alkylene group is 1 to 20, but it is preferably 1 to 12, more preferably 1 to 8, still more preferably 1 to 4, still much more preferably 1, 2 or 4, and particularly preferably 2.

In the lubricating oil composition of one embodiment of the present invention, the component (C) preferably contains one or more sulfur-phosphorus-based compounds (C1) selected from a sulfur atom-containing phosphoric acid ester and a sulfur atom-containing phosphorous acid ester, from the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance.

In the lubricating oil composition of one embodiment of the present invention, the content of the component (C1) is preferably 60 to 100 mass %, more preferably 70 to 100 mass %, more preferably 80 to 100 mass %, still more preferably 90 to 100 mass %, still much more preferably 95 to 100 mass %, and particularly preferably 98 to 100 mass %, based on the total amount (100 mass %) of the component (C) contained in the lubricating oil composition, from the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance.

As the sulfur atom-containing phosphoric acid ester and the sulfur atom-containing phosphorous acid ester, a sulfur atom-containing phosphoric acid ester and a sulfur atom-containing phosphorous acid ester each of which has a group represented by the aforementioned formula (ii) can be mentioned.

From the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance, the component (C1) used in one embodiment of the present invention is preferably a sulfur atom-containing phosphorus acid ester having a group represented by the formula (ii), and is more preferably one or more selected from a compound (C11) represented by the following general formula (c-11) and a compound (C12) represented by the following general formula (c-12).

In the formulae (c-11) and (c-12), R^(A11), R^(A21) and R^(A22) are each independently a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

The alkyl group may be a straight-chain alkyl group or may be a branched chain alkyl group, but it is preferably a straight-chain alkyl group.

The number of carbon atoms of the alkyl group is 1 to 20, but it is preferably 2 to 18, more preferably 4 to 16, still more preferably 6 to 12, and still much more preferably 8 to 10.

a1, a2 and a3 are each independently an integer of 1 to 20, but preferably an integer of 1 to 12, more preferably an integer of 1 to 8, still more preferably an integer of 1 to 4, still much more preferably 1, 2 or 4, and particularly preferably 2.

In the lubricating oil composition of one embodiment of present invention, the component (C) still more preferably contains both of the compound (C11) represented by the general formula (c-11) and the compound (C12) represented by the general formula (c-12), from the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance.

In one embodiment of the present invention, the content ratio by mass of the compound (C11) to the compound (C12), [(C11)/(C12)], is preferably 1/20 to 20/1, more preferably 1/16 to 10/1, more preferably 1/14 to 5/1, still more preferably 1/12 to 2/1, still much more preferably 1/11 to 1/1, and particularly preferably 1/10 to ½.

The acid phosphoric acid ester and the acid phosphorous acid ester each of which is used as the component (C) in one embodiment of the present invention may be each in the form of an amine salt.

The amine to form the amine salt is preferably a compound represented by the following general formula (c-i). The amine may be used singly, or may be used in combination of two or more.

(R^(x))_(r)—N—(H)_(3-r)  (C-i)

In the general formula (c-i), r is an integer of 1 to 3, and is preferably 1.

Each R^(x) is independently an alkyl group having 6 to 18 carbon atoms, an alkenyl group having 6 to 18 carbon atoms, an aryl group having 6 to 18 carbon atoms, or a hydroxyalkyl group having 6 to 18 carbon atoms.

When multiple R^(x) are present, the multiple R^(x) may be the same as one another, or may be different from one another.

Examples of the alkyl group having 6 to 18 carbon atoms, the alkenyl group having 6 to 18 carbon atoms and the aryl group having 6 to 18 carbon atoms capable of being selected as R^(x) include groups having carbon atoms of the above ranges among the groups given as examples of the alkyl group, the alkenyl group and the aryl group capable of being selected as R²¹ to R²³.

As the hydroxyalkyl group having 6 to 18 carbon atoms, a group wherein a hydrogen atom of an alkyl group having 6 to 18 carbon atoms is substituted by a hydroxyl group can be mentioned, and specific examples thereof include a hydroxyhexyl group, a hydroxyoctyl group, a hydroxydodecyl group and a hydroxytridecyl group.

From the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance, the content of the component (C) in the lubricating oil composition of one embodiment of the present invention is preferably 0.01 mass % or more, more preferably 0.05 mass % or more, still more preferably 0.07 mass % or more, still much more preferably 0.10 mass % or more, and particularly preferably 0.15 mass % or more, or may be 0.17 mass % or more, 0.20 mass % or more, 0.23 mass % or more, 0.25 mass % or more, 0.27 mass % or more, or 0.30 mass % or more, and it is preferably 3.0 mass % or less, more preferably 2.5 mass % or less, still more preferably 2.0 mass % or less, still much more preferably 1.5 mass % or less, and particularly preferably 1.2 mass % or less, or may be 1.0 mass % or less, 0.95 mass % or less, 0.90 mass % or less, 0.85 mass % or less, 0.80 mass % or less, 0.75 mass % or less, 0.70 mass % or less, 0.65 mass % or less, 0.60 mass % or less, 0.55 mass % or less, or 0.50 mass % or less, based on the total amount (100 mass %) of the lubricating oil composition.

From the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance, the content of the component (C) in terms of phosphorus atoms in the lubricating oil composition of one embodiment of the present invention is preferably 30 ppm by mass or more, more preferably 50 ppm by mass or more, more preferably 70 ppm by mass or more, more preferably 100 ppm by mass or more, still more preferably 120 ppm by mass or more, still more preferably 150 ppm by mass or more, still more preferably 180 ppm by mass or more, still much more preferably 200 ppm by mass or more, still much more preferably 220 ppm by mass or more, still much more preferably 250 ppm by mass or more, and particularly preferably 270 ppm by mass or more, and is preferably 800 ppm by mass or less, more preferably 700 ppm by mass or less, still more preferably 600 ppm by mass or less, still much more preferably 500 ppm by mass or less, and particularly preferably 450 ppm by mass or less, or may be 420 ppm by mass or less, 400 ppm by mass or less, 380 ppm by mass or less, 370 ppm by mass or less, 360 ppm by mass or less, or 350 ppm by mass or less, based on the total amount (100 mass %) of the lubricating oil composition.

In the present specification, the content of phosphorus atoms means a value measured in accordance with JPI-5S-38-92.

From the viewpoint of obtaining a lubricating oil composition having been further improved in wear resistance, the content of the component (C) in terms of sulfur atoms in the lubricating oil composition of one embodiment of the present invention is preferably 50 ppm by mass or more, more preferably 70 ppm by mass or more, more preferably 100 ppm by mass or more, more preferably 120 ppm by mass or more, still more preferably 150 ppm by mass or more, still more preferably 180 ppm by mass or more, still more preferably 200 ppm by mass or more, still much more preferably 220 ppm by mass or more, still much more preferably 250 ppm by mass or more, still much more preferably 270 ppm by mass or more, and particularly preferably 300 ppm by mass or more, and is preferably 800 ppm by mass or less, more preferably 700 ppm by mass or less, still more preferably 600 ppm by mass or less, still much more preferably 500 ppm by mass or less, and particularly preferably 450 ppm by mass or less, or may be 420 ppm by mass or less, 400 ppm by mass or less, 380 ppm by mass or less, 370 ppm by mass or less, 360 ppm by mass or less, or 350 ppm by mass or less, based on the total amount (100 mass %) of the lubricating oil composition.

In the present specification, the content of sulfur atoms means a value measured in accordance with JPI-5S-38-92.

In the lubricating oil composition of one embodiment of the present invention, the content of a sulfur atom-free acid phosphoric acid ester in terms of phosphorus atoms may be less than 100 ppm by mass, less than 50 ppm by mass, less than 10 ppm by mass, less than 8 ppm by mass, less than 5 ppm by mass, less than 3 ppm by mass, or less than 1 ppm by mass, based on the total amount (100 mass %) of the lubricating oil composition.

In the lubricating oil composition of one embodiment of the present invention, the content of a sulfur atom-free neutral phosphoric acid ester in terms of phosphorus atoms may be less than 50 ppm by mass, less than 10 ppm by mass, less than 8 ppm by mass, less than 5 ppm by mass, less than 3 ppm by mass, or less than 1 ppm by mass, based on the total amount (100 mass %) of the lubricating oil composition.

<Various Additives Other than Components (B) to (C)>

The lubricating oil composition of one embodiment of the present invention may contain various additives other than the components (B) to (C) when needed as long as the effects of the present invention are not impaired.

Examples of such various additives include an antioxidant, a metal-based detergent, an ashless dispersant, a metal deactivator, an anti-rust agent, an anti-foaming agent, and a pour point depressant.

These lubricating oil additives may be each used singly, or may be each used in combination of two or more.

The contents of these lubricating oil additives can be each appropriately adjusted as long as the effects of the present invention are not impaired, and the contents of the additives are each independently usually 0.001 to 15 mass %, preferably 0.005 to 10 mass %, and more preferably 0.01 to 5 mass %, based on the total amount (100 mass %) of the lubricating oil composition.

[Antioxidant]

The lubricating oil composition of one embodiment of the present invention may further contain an antioxidant. The antioxidant may be used singly, or may be used in combination of two or more.

Examples of the antioxidants used in one embodiment of the present invention include amine-based antioxidants, such as alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine; and phenol-based antioxidants, such as 2,6-di-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate.

In the lubricating oil composition of one embodiment of the present invention, it is preferable to use, as the antioxidant, a combination of an amine-based antioxidant and a phenol-based antioxidant. [Metal-based detergent]

The lubricating oil composition of one embodiment of the present invention may further contain a metal-based detergent. The metal-based detergent may be used singly, or may be used in combination of two or more.

Examples of the metal-based detergents used in one embodiment of the present invention include metal salts, such as a metal sulfonate, a metal salicylate, and a metal phenate. The metal to constitute the metal salts is preferably a metal atom selected from alkali metals and alkaline earth metals, more preferably sodium, calcium, magnesium or barium, and still more preferably calcium.

In the lubricating oil composition of one embodiment of the present invention, the metal-based detergent preferably contains one or more selected from calcium sulfonate, calcium salicylate and calcium phenate, and more preferably contains calcium sulfonate.

The content of the calcium sulfonate is preferably to 100 mass %, more preferably 60 to 100 mass %, still more preferably 70 to 100 mass %, and still much more preferably 80 to 100 mass %, based on the total amount (100 mass %) of the metal-based detergent contained in the lubricating oil composition.

The base number of the metal-based detergent is preferably 0 to 600 mgKOH/g.

In the lubricating oil composition of one embodiment of the present invention, however, the metal-based detergent is preferably an overbased metal-based detergent having a base number of 100 mgKOH/g or more.

The base number of the overbased metal-based detergent is 100 mgKOH/g or more, but it is preferably 150 to 500 mgKOH/g, and more preferably 200 to 450 mgKOH/g.

In the present specification, the “base number” means a base number measured by perchloric acid method in accordance with JIS K2501:2003 “Petroleum products and lubricants—Determination of neutralization number”, 7.

[Ashless Dispersant]

From the viewpoint of improving dispersibility of the component (B) and the component (C), the lubricating oil composition of one embodiment of the present invention may further contain an ashless dispersant. The ashless dispersant may be used singly, or may be used in combination of two or more.

The ashless dispersant used in one embodiment of the present invention is preferably an alkenyl succinimide, and examples thereof include an alkenyl bis-succinimide represented by the following general formula (d-1) and an alkenyl monosuccinimide represented by the following general formula (d-2).

In the general formulae (d-1) and (d-2), R^(a1), R^(a2) and R^(a3) are each independently an alkenyl group having a mass-average molecular weight (Mw) of 500 to 3000 (preferably 900 to 2500).

Examples of the alkenyl groups capable of being selected as R^(a1), R^(a2) and R^(a3) include a polybutenyl group, a polyisobutenyl group and an ethylene-propylene copolymer, and among these, a polybutenyl group or a polyisobutenyl group is preferable.

R^(b1), R^(b2) and R^(b3) are each independently an alkylene group having 2 to 5 carbon atoms.

z1 is an integer of 0 to 10, preferably an integer of 1 to 4, and more preferably 2 or 3.

z2 is an integer of 1 to 10, preferably an integer of 2 to 5, and more preferably 3 or 4.

The compound represented by the general formula (d-1) or (d-2) may be a modified alkenyl succinimide obtained by reacting this compound with one or more selected from a boron compound, an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an epoxy compound and an organic acid.

[Metal Deactivator]

The lubricating oil composition of one embodiment of the present invention may further contain a metal deactivator. The metal deactivator may be used singly, or may be used in combination of two or more.

Examples of the metal deactivators used in one embodiment of the present invention include a benzotriazole-based compound, a tolyltriazole-based compound, an imidazole-based compound, and a pyrimidine-based compound.

[Anti-Rust Agent]

The lubricating oil composition of one embodiment of the present invention may further contain an anti-rust agent. The anti-rust agent may be used singly, or may be used in combination of two or more.

Examples of the anti-rust agents used in one embodiment of the present invention include a fatty acid, an alkenyl succinic acid half ester, a fatty acid soap, an alkyl sulfonic acid salt, a polyhydric alcohol fatty acid ester, a fatty acid amine, oxidized paraffin, and an alkyl polyoxyethylene ether.

[Anti-Foaming Agent]

The lubricating oil composition of one embodiment of the present invention may further contain an anti-foaming agent. The anti-foaming agent may be used singly, or may be used in combination of two or more.

Examples of the anti-foaming agents used in one embodiment of the present invention include a silicone oil, a fluorosilicone oil, and a fluoroalkyl ether.

[Pour Point Depressant]

The lubricating oil composition of one embodiment of the present invention may further contain a pour point depressant. The pour point depressant may be used singly, or may be used in combination of two or more.

Examples of the pour point depressants used in one embodiment of the present invention include an ethylene-vinyl acetate copolymer, a condensate of chlorinated paraffin and naphthalene, a condensate of chlorinated paraffin and phenol, polymethacrylate, and polyalkylstyrene.

<Method for Producing Lubricating Oil Composition>

The method for producing a lubricating oil composition of one embodiment of the present invention is not particularly limited, but from the viewpoint of productivity, preferable is a method having

-   -   a step of adding the component (B) to the component (A) and         preparing the lubricating oil composition in such a manner that         a content of a sulfurized olefin is less than 0.20 mass % based         on the total amount of the lubricating oil composition and that         a kinematic viscosity of the lubricating oil composition at         100° C. is 2.1 mm²/s or more and less than 5.0 mm²/s.

When the component (B) is added to the component (A), it is preferable to add the component (C) and other various additives than the components (B) to (C), when needed.

Here, preferred compounds and amounts of the components (A), (B) and (C), and various additives are as previously described.

[Properties of Lubricating Oil Composition]

The viscosity index of the lubricating oil composition of one embodiment of the present invention is preferably 80 or more, more preferably 90 or more, still more preferably 100 or more, and still much more preferably 110 or more.

In the lubricating oil composition of one embodiment of the present invention, the content of molybdenum atoms may be less than 100 ppm by mass, less than 50 ppm by mass, less than 30 ppm by mass, less than ppm by mass, less than 10 ppm by mass, less than 7 ppm by mass, less than 5 ppm by mass, less than 3 ppm by mass, or less than 2 ppm by mass, based on the total amount (100 mass %) of the lubricating oil composition.

In the present specification, the content of molybdenum means a value measured in accordance with JPI-5S-38-92.

The flash point of the lubricating oil composition of one embodiment of the present invention is preferably 160° C. or more, more preferably 164° C. or more, still more preferably 170° C. or more, still much more preferably 174° C. or more, and particularly preferably 180° C. or more, and may be 300° C. or less, 280° C. or less, 260° C. or less, or 250° C. or less, from the viewpoint of obtaining a lubricating oil composition having excellent safety.

In the present specification, the flash point means a value measured by Cleveland open-cup (COC) method in accordance with ASTM D92.

The aniline point of the lubricating oil composition of one embodiment of the present invention is preferably 80 to 120° C., more preferably 85 to 118° C., still more preferably 90 to 115° C., still much more preferably 95 to 112° C., and particularly preferably 100 to 110° C., from the viewpoint of improving solubility of the component (B).

In the present specification, the aniline point means a value measured in accordance with ASTM D611.

Regarding the lubricating oil composition of one embodiment of the present invention, a surface temperature of a silver rod, which is measured 12 seconds after the silver rod having been heated to 200° C. is placed in 200 mL of the lubricating oil composition having been heated to 80° C. as described in Examples described later in accordance with JIS K2242, is preferably 150.0° C. or less, more preferably 149.0° C. or less, still more preferably 148.0° C. or less, still much more preferably 147.0° C. or less, and particularly preferably 146.0° C. or less.

Regarding the lubricating oil composition of one embodiment of the present invention, a load stage that is measured under the conditions described in Examples described later in accordance with ASTM D5182 when scuffing has occurred is preferably 5 or more, more preferably 6 or more, still more preferably 7 or more, and still much more preferably 8 or more.

Regarding the lubricating oil composition of one embodiment of the present invention, a volume resistivity of the lubricating oil composition, which is measured under the conditions described in Examples described later in accordance with JIS C2101, is preferably 2.0×10⁷ Ω·m or more, more preferably 2.2×10⁷ Ω·m or more, still more preferably 2.4×10⁷ Ω·m or more, still much more preferably 2.8×10⁷ Ω·m or more, and particularly preferably 3.0×10⁷ Ω·m or more, and is usually 1.0×10⁹ or less.

Regarding the lubricating oil composition of one embodiment of the present invention, an elution amount of copper for the lubricating oil composition, which is determined when ISOT test in accordance with JIS K2514 has been carried out using a copper fragment as a catalyst at a temperature of 150° C. for 72 hours as described in Examples described later, is preferably 70 ppm by mass or less, more preferably 60 ppm by mass or less, still more preferably 50 ppm by mass or less, still much more preferably 40 ppm by mass or less, and particularly preferably 35 ppm by mass or less.

In the present specification, the elution amount of copper means a value measured in accordance with JPI-5S-38-92.

[Use Application of Lubricating Oil Composition]

The lubricating oil composition of one preferred embodiment of the present invention can be improved in cooling performance, scuffing resistance and insulation properties in a balanced manner.

Taking such characteristics into consideration, the lubricating oil composition of one embodiment of the present invention can be preferably used for lubrication in mechanisms, such as a torque converter, a wet clutch, a gear bearing mechanism, an oil pump and a hydraulic control mechanism, which are incorporated in various apparatuses, such as an engine, a transmission, a speed reducer, a compressor and a hydraulic system. The lubricating oil composition of one embodiment of the present invention is preferably used for lubrication of a speed reducer among these.

When the aforementioned characteristics of the lubricating oil composition of one embodiment of the present invention are taken into consideration, the present invention can also provide the following [1] and [2].

-   -   [1] A speed reducer using a lubricating oil composition         comprising a base oil (A) and a thiadiazole-based compound (B),         having a sulfurized olefin content of less than 0.20 mass %, and         having a kinematic viscosity at 100° C. of 2.1 mm²/s or more and         less than 5.0 mm²/s.     -   [2] Use of a lubricating oil composition, in which a lubricating         oil composition comprising a base oil (A) and a         thiadiazole-based compound (B), having a sulfurized olefin         content of less than 0.20 mass %, and having a kinematic         viscosity at 100° C. of 2.1 mm²/s or more and less than 5.0         mm²/s is applied to lubrication of a speed reducer.

Preferred embodiments of the lubricating oil composition described in the above [1] and [2] are as previously described.

EXAMPLES

Next, the present invention will be described in much more detail with reference to Examples, but the present invention is in no way limited to these Examples. Measuring methods for various properties are as follows.

(1) Kinematic Viscosity, Viscosity Index

The kinematic viscosity and viscosity index were measured and calculated in accordance with JIS K2283:2000.

(2) Content of Sulfur Atoms

The content was measured in accordance with JIS K2541-6:2013.

(3) Content of Nitrogen Atoms

The content was measured in accordance with JIS K2609.

(4) Contents of Phosphorus Atoms and Molybdenum

The contents were measured in accordance with JPI-5S-38-92.

(5) Base Number (Perchloric Acid Method)

The base number was measured in accordance with JIS K2501:2003 (perchloric acid method).

(6) Weight-Average Molecular Weight (Mw)

Using a gel permeation chromatograph apparatus (manufactured by Agilent Technologies, Inc., “1260 model HPLC”), the weight-average molecular weight was measured under the following conditions, and a value measured in terms of standard polystyrene was used.

(Measurement Conditions)

-   -   Column: sequentially connected two of “Shodex LF404”.     -   Column temperature: 35° C.     -   Developing solvent: chloroform     -   Flow rate: 0.3 mL/min

(7) Flash Point

The flash point was measured by Cleveland open-cup (COC) method in accordance with ASTM D92.

(8) Aniline Point

The aniline point was measured in accordance with ASTM D611.

Examples 1 to 9, Comparative Examples 1 to 4

A base oil and various additives of types shown in Table 1 were added and mixed in amounts shown in Tables 1 and 2, thereby preparing each lubricating oil composition. Details of each component used in the preparation of the lubricating oil composition are as follows. In any of the lubricating oil compositions, the content of molybdenum atoms was less than 2 ppm by mass.

<Base Oil>

-   -   “Mineral oil (1)”: 60N hydrocracked mineral oil, 100° C.         kinematic viscosity=2.2 mm²/s, viscosity index=108.     -   “Mineral oil (2)”: 100N hydrocracked mineral oil, 100° C.         kinematic viscosity=4.2 mm²/s, viscosity index=122.     -   “Mineral oil (3)”: 150N hydrocracked mineral oil, 100° C.         kinematic viscosity=6.0 mm²/s, viscosity index=132.     -   “PAO (1)”: poly-α-olefin, 100° C. kinematic viscosity=1.8 mm²/s.     -   “PAO (2)”: poly-α-olefin, 100° C. kinematic viscosity=2.0 mm²/s.     -   “PAO (3)”: poly-α-olefin, 100° C. kinematic viscosity=3.9 mm²/s,         viscosity index=120.

<Sulfur-Based Compound>

-   -   “Thiadiazole (branched chain)”:         2,5-bis(1,1-dimethylheptyldithio)-1,3,4-thiadiazole, thiadiazole         of the aforementioned general formula (b-1) wherein m=n=2, and         R¹ and R² are each a 1,1-dimethylheptyl group; sulfur atom         content=33.3 mass %, nitrogen atom content=6.4 mass %.     -   “Thiadiazole (straight-chain)”:         2,5-bis(n-octyldithio)-1,3,4-thiadiazole, thiadiazole of the         aforementioned general formula (b-1) wherein m=n=2, and R¹ and         R² are each a n-octyl group; sulfur atom content=34 mass %,         nitrogen atom content=4.2 mass %.     -   “Sulfurized olefin”: sulfurized olefin represented by the         aforementioned general formula (i); sulfur atom content: 43 mass         %.

<Sulfur-Phosphorus-Based Compound>

-   -   “Sulfur-phosphorus-based compound (1)”: sulfur atom-containing         phosphorous acid ester of the aforementioned general formula         (c-11) wherein a1=2, and R^(A11)=n-octyl group.     -   “Sulfur-phosphorus-based compound (2)”: sulfur atom-containing         phosphorous acid ester of the aforementioned general formula         (c-12) wherein a2=a3=2, and R^(A21), R^(A22)=n-octyl group.

Other Additives

-   -   “Pour point depressant”: polymethacrylate-based pour point         depressant.     -   “Additive mixture”: additive mixture obtained by mixing the         following additives and diluting the mixture with 70N         hydrocracked mineral oil.

Phenol-Based Antioxidant (Hindered Phenol)

-   -   Amine-based antioxidant (alkylated diphenylamine having 9 carbon         atoms)     -   Calcium sulfonate (base number (perchloric acid method)=300         mgKOH/g)     -   Succinic acid bisimide having polybutenyl group of M_(w)=960

Benzotriazole

Glycerol Fatty Acid Ester

Silicone-Based Anti-Foaming Agent

Regarding the lubricating oil compositions prepared, the kinematic viscosity, viscosity index, flash point and aniline point were measured or calculated, and the following test was carried out. The results of them are set forth in Tables 1 and 2.

(1) Cooling Performance Test

In accordance with “6.2 Testing method for cooling performance (Method A: surface temperature measuring method)” of JIS K2242, a silver rod having been heated to 200° C. was placed in 250 mL of a sample oil having been heated to 80° C., and 12 seconds later, a surface temperature of the silver rod was measured. It can be said that the lower the surface temperature of the silver rod is, the better the cooling performance of the lubricating oil composition becomes.

(2) FZG Scuffing Test (A10/16.6R/90)

A load was stepwise increased based on the regulations using an A10 type gear under the conditions of a sample oil temperature of 90° C., a rotational speed of 2900 rpm and an operating time of about 7.5 minutes in accordance with ASTM D5182, and when scuffing occurred, a stage of the load was determined. It can be said that the larger the value of the stage is, the better the gear scuffing resistance of the lubricating oil composition becomes.

(3) Insulation Property Test

A volume resistivity of a sample oil was measured under the test conditions of a measurement temperature of 80° C., an applied voltage of 250 V, and a measurement time of 1 minute in accordance with JIS C2101. It can be said that the larger the value of the volume resistivity is, the better the insulation properties of the lubricating oil composition become.

(4) Copper Elution Test

Using a copper fragment and an iron fragment as catalysts, ISOT test in accordance with JIS K2514 was carried out at a temperature of 150° C. for 72 hours to degrade a sample oil. For the degraded sample oil, an elution amount of copper (unit: ppm by mass) was measured by the method in accordance with JPI-5S-38-92. It can be said that the smaller the value of the elution amount of copper is, the higher the copper elution suppressing effect of the lubricating oil composition becomes.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Base oil Mineral oil (1) mass % 67.00 20.00 Mineral oil (2) mass % 27.50 74.50 Mineral oil (3) mass % PAO (1) mass % PAO (2) mass % 94.50 47.10 7.60 94.60 PAO (3) mass % 47.50 87.00 Sulfur- Thiadiazole (branched chain) mass % 0.40 0.30 0.30 0.30 0.30 0.30 based Thiadiazole (straight-chain) mass % compound Sulfurized olefin mass % Sulfur- Sulfur-phosphorus-based mass % 0.27 0.27 0.27 0.27 0.27 0.27 phosphorus- compound (1) based Sulfur-phosphorus-based mass % 0.03 0.03 0.03 0.03 0.03 0.03 compound compound (2) Other Pour point depressant mass % 0.10 0.10 additives Additive mixture mass % 4.80 4.80 4.80 4.80 4.80 4.80 Total mass % 100.00 100.00 100.00 100.00 100.00 100.00 Content of sulfur atoms derived from ppm by 1333 1000 1000 1000 1000 1000 thiadiazole-based compound mass Content of nitrogen atoms derived from ppm by 256 192 192 192 192 192 thiadiazole-based compound mass Content of sulfurized olefin mass % <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Total content of phosphorus atoms derived ppm by 300 300 300 300 300 300 from sulfur-phosphorus-based compounds (1) mass and (2) Total content of sulfur atoms derived from ppm by 322 322 322 322 322 322 sulfur-phosphorus-based compounds (1) and mass (2) Various 40° C. kinematic viscosity mm²/s 7.37 11.48 17.77 11.52 17.62 7.37 properties 100° C. kinematic viscosity mm²/s 2.22 3.00 4.03 3.02 3.99 2.22 Viscosity index mm²/s 107 118 127 119 125 107 Flash point ° C. 174 172 192 184 214 174 Aniline point ° C. 105 104 111 112 118 105 Various (1) Cooling performance test, ° C. 145.2 148.8 149.6 146.6 148.6 145.2 tests Surface temperature of silver rod (2) FZG scuffing test, Stage — 7 8 9 7 8 6 (3) Insulation property test, ×10⁷ Ωm 2.3 3.2 4.0 2.9 3.8 2.5 Volume resistivity (4) Copper elution test, Elution ppm by 34 29 30 31 30 28 amount of copper mass

TABLE 2 Comp. Comp. Comp. Comp. Ex. 7 Ex. 8 Ex. 9 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Base oil Mineral oil (1) mass % 67.00 67.00 67.00 67.00 67.00 Mineral oil (2) mass % 27.60 27.00 27.49 27.56 27.80 Mineral oil (3) mass % 94.50 PAO (1) mass % 94.60 PAO (2) mass % PAO (3) mass % Sulfur- Thiadiazole (branched chain) mass % 0.20 0.80 0.00 0.30 0.30 based Thiadiazole (straight-chain) mass % 0.31 compound Sulfurized olefin mass % 0.24 Sulfur- Sulfur-phosphorus-based mass % 0.27 0.27 0.27 0.27 0.27 0.27 0.27 phosphorus- compound (1) based Sulfur-phosphorus-based mass % 0.03 0.03 0.03 0.03 0.03 0.03 0.03 compound compound (2) Other Pour point depressant mass % 0.10 0.10 0.10 0.10 0.10 0.10 additives Additive mixture mass % 4.80 4.80 4.80 4.80 4.80 4.80 4.80 Total mass % 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Content of sulfur atoms derived from ppm by 667 2667 1000 0 0 1000 1000 thiadiazole-based compound mass Content of nitrogen atoms derived from ppm by 128 512 130 0 0 192 192 thiadiazole-based compound mass Content of sulfurized olefin mass % <0.001 <0.001 <0.001 0.24 <0.001 <0.001 <0.001 Total content of phosphorus atoms derived ppm by 300 300 300 300 300 300 300 from sulfur-phosphorus-based compounds mass (1) and (2) Total content of sulfur atoms derived from ppm by 322 322 322 322 322 322 322 sulfur-phosphorus-based compounds (1) and mass (2) Various 40° C. kinematic viscosity mm²/s 11.47 11.56 11.45 11.43 11.43 6.20 34.54 properties 100° C. kinematic viscosity mm²/s 3.00 3.02 3.00 3.00 3.00 1.97 6.32 Viscosity index mm²/s 118 119 119 119 119 115 135 Flash point ° C. 172 172 172 172 172 158 240 Aniline point ° C. 104 104 104 104 104 102 121 Various (1) Cooling performance test, ° C. 148.9 148.8 148.7 148.8 148.8 144.3 153.4 tests Surface temperature of silver rod (2) FZG scuffing test, Stage — 7 7 8 4 4 4 8 (3) Insulation property test, ×10⁷ 3.5 2.8 3.6 3.7 3.9 1.7 6.3 Volume resistivity Ωm (4) Copper elution test, Elution ppm by 18 46 209 76 10 32 30 amount of copper mass

From Table 1 and Table 2, the results for the lubricating oil compositions of Examples 1 to 9 were superior in cooling performance, scuffing resistance and insulation properties in a balanced manner despite the low viscosities. On the other hand, the results for the lubricating oil compositions of Comparative Examples 1 to 2 were inferior in scuffing resistance, and the result for the lubricating oil composition of Comparative Example 3 was inferior in not only scuffing resistance but also insulation properties. The result for the lubricating oil composition of Comparative Example 4 was inferior in cooling performance though the scuffing resistance was good. 

1. A lubricating oil composition comprising a base oil (A) and a thiadiazole-based compound (B), wherein a content of a sulfurized olefin is less than 0.20 mass % based on the total amount of the lubricating oil composition, and a kinematic viscosity of the lubricating oil composition at 100° C. is 2.1 mm²/s or more and less than 5.0 mm²/s.
 2. The lubricating oil composition according to claim 1, wherein the component (B) comprises a thiadiazole-based compound (B1) having a branched chain alkyl group.
 3. The lubricating oil composition according to claim 2, wherein a number of carbon atoms of the branched chain alkyl group of the component (B1) is 5 or more.
 4. The lubricating oil composition according to claim 1, wherein the component (B) comprises a compound represented by any one of the following general formulae (b-1) to (b-4):

wherein R¹ and R² are each independently a hydrocarbon group, and m and n are each independently an integer of 1 to
 10. 5. The lubricating oil composition according to claim 4, wherein R¹ and R² are each independently a branched chain alkyl group having 5 or more carbon atoms.
 6. The lubricating oil composition according to claim 1, wherein a content of a compound represented by the following general formula (b-x) is less than 10 mass % based on the total amount of the component (B) contained in the lubricating oil composition,

wherein R^(a) is a hydrogen atom or a methyl group, R^(b) is an alkyl group having 1 to 4 carbon atoms, and p is 0 or
 1. 7. The lubricating oil composition according to claim 1, wherein a content of the component (B) is 0.01 to 3.0 mass % based on the total amount of the lubricating oil composition.
 8. The lubricating oil composition according to claim 1, wherein a content of the component (B) is 0.10 to 1.0 mass % based on the total amount of the lubricating oil composition.
 9. The lubricating oil composition according to claim 1, wherein the component (A) is one or more selected from mineral oils classified in Group II and Group III of API base oil categories, and synthetic oils.
 10. The lubricating oil composition according to claim 1, further comprising one or more phosphorus-based compounds (C) selected from a phosphoric acid ester and a phosphorous acid ester.
 11. The lubricating oil composition according to claim 10, wherein the component (C) comprises one or more sulfur-phosphorus-based compounds (C1) selected from a sulfur atom-containing phosphoric acid ester and a sulfur atom-containing phosphorous acid ester.
 12. A speed reducer lubrication composition, comprising the lubricating oil composition according to claim
 1. 13. A method of lubricating a speed reducer comprising applying the lubricating oil composition of claim 1 to the speed reducer.
 14. A method for producing the lubricating oil composition according to claim 1, comprising: adding the thiadiazole-based compound (B) to the base oil (A), and preparing the lubricating oil composition in such a manner that the content of the sulfurized olefin is less than 0.20 mass % based on the total amount of the lubricating oil composition, and that the kinematic viscosity of the lubricating oil composition at 100° C. is 2.1 mm²/s or more and less than 5.0 mm²/s. 